A variety of optical equipment or devices in the general class of telescopes have been used for many years for observing terrestrial and extraterrestrial objects. Telescopic equipment has long been used by amateur and professional observers alike in remote locations to gather general information and data about various stellar or planetary bodies.
The average person thinks of telescopes in terms of the traditional tubular, direct focal optics, Galileo-type telescope. However, while such telescopes allow reasonable resolution or magnification for observation of nearby extraterrestrial objects such as the moon or planets, they are inadequate for refined observations and tracking of more distant objects. A professional or true hobbyist astronomical observer generally employs a much more complex, reflective-type telescopic apparatus. The use of a telescope configured as a cassegrain-type reflector allows greater light capture and higher resolution for improved observations of very small astronomical objects.
At the same time, it is generally necessary to utilize high powered telescopes in a fairly remote location, since "skyglow" from city lights tends to obscure a majority of the distant (visually small) astronomical objects. In addition, it is preferred to make observations from as high an altitude as possible since the density and particulate content of the Earth's lower atmosphere distorts incoming light making accurate detailed observations more difficult. To overcome or minimize such problems, telescope owners often use their equipment in generally remote and possibly high altitude locations. Therefore, a large class of reflective optics telescopes are made for ease of portability.
Portable telescopes of the reflective-type generally have an internal volume on the order of one or more cubic feet and exterior dimensions on the order of six to twenty-four inches in diameter and eighteen to twenty-four or more inches long. The exterior housing or main structure of such telescopes is generally constructed from cast aluminum on the order of 0.125 or more inches thick. Generally there are mounting brackets, counter balance supports, swivel joints, and other associated hardware attached to the telescope which are made from steel, brass, or similar materials. While this presents a reasonably rigid but lightweight structure, it does present a serious problem because of the nature of the remote application or environment.
Most of these telescopes are used in remote locations which have no shelter or environmental control. That means, that the telescope is exposed to the surrounding atmospheric conditions which includes the relative temperature, humidity, and atmospheric contaminates. Since most astronomical observations are by definition made at night, this means that the local temperature of the environment, and the telescope, is generally fairly low. At higher altitudes this is exaggerated by the fact that the temperature generally drops up to five degrees for every additional thousand feet in elevation. Therefore, especially during fall and winter seasons, a telescope may be consistently utilized in temperature below twenty to forty degrees Fahrenheit.
At these temperatures, the large amount of metal utilized in the telescope structure tends to act as a collection surface for moisture. This is due to the natural effect of a cold surface absorbing or trapping moisture due to condensation on the surface. In the past, moisture deposition on the exterior surface of a telescope has been considered little more than a nuisance which can be handled by the judicious use of a few rags, clothes, or telescope covers. The exterior surfaces of any optics or telescope lenses are generally protected by lens covers when not in use and do not collect that large an amount of moisture during use. They can also be easily cleaned. However, more recently it has been discovered that moisture accumulation and deposition is damaging the internal optical surfaces of telescopes. This is due primarily to the utilization of access ports for lenses and camera attachments which allow ready insertion and removal of alternate lenses or cameras for use in observations.
In most of the reflector-type telescopes the focal lens assembly through which reflectors and sub-reflectors present an image are mounted on a tubular assembly which is in turn mounted along a central axis of the telescope. In order to provide adjustability, cleaning, and optical modification of the telescope focusing characteristics, this lens assembly is generally removable. That is, it is mounted through an access port and may be locked in place using a simple friction or slip ring-type fitting which allows easy removal. This type of lens attachment has the advantage that various pieces of photographic equipment can also be inserted in place of the final lenses to capture observed images for later analysis. While this is a standard approach in the art of telescope construction and operation, it does present a serious drawback in the presence of significant amounts of moisture or high humidity.
When the lens assembly is removed from the telescope in a cold environment, which is frequently done to change lenses or insert photographic equipment, moist air is allowed to enter the interior of the telescope. Since the telescope comprises a largely metallic housing and glass optical surfaces, the moist air contacts a large surface area on which moisture readily condenses under typical operating temperatures for telescopes. Therefore, in the normal operation of telescopes a small amount of moisture is often deposited on the inside surfaces during setup, disassembly, or change out activities.
It has been discovered that this moisture does not tend to impair the focal capabilities or light gathering capabilities of the telescope initially or rapidly. A telescope user is not likely to readily notice the presence of a fine layer of moisture. This is typically enhanced by the fact that the moisture is often deposited at the point of disassembly and will dry out during storage of the telescope. However, if the moisture is allowed to reside on the optics for any period of time, even if it evaporates, it damages the optical coatings. The damage results from several processes.
First, the atmosphere is increasingly full of contaminates or pollutants which tend to be either slightly acidic or otherwise reactive with most optical coatings. Atmospheric moisture collects or concentrates these contaminates and deposits them in a fine coating on the optical surfaces where they will slowly degrade the optical coatings. Second, the water itself may naturally contain many minerals or other components which build up over time after many depositions and begin to alter the optical qualities of lenses and reflectors.
It has been discovered with careful observation that a pattern of small "pits" appears on lenses after many exposures to moisture, leading to severe degradation of resolution and light gathering characteristics. It is very expensive to either replace optical coatings or periodically disassemble the entire telecope and clean and maintain the inside. Telescope disassembly and repair is not a do it yourself activity. An untrained individual will ruin the fine alignment and collimation required for high resolution.
What is needed then is a method of preventing the build up of moisture or removing existing moisture that enters the interior of a telescope when an access port or other opening allows substantial free entry of air.
In the past, this might have been accomplished by manufacturing the telescope with some form of desiccant permanently mounted inside. This technique has been used in some binoculars or similar optical equipment. Such a technique is disclosed in U.S. Pat. No. 2,399,971 where small packages of a desiccant are placed in corners of the housing for binoculars at the point of assembly. This technique initially controls moisture deposition on interior optical surfaces at the time of manufacture. However, this technique is useful only in the situation where the housing remains sealed and only a small amount of moisture penetrates the seal. In the typical binocular type application the housing is sealed from the moment of manufacture and never opened again unless damaged or major maintenance is required.
In the case of reflective-type telescopes, the interior and any desiccant stored therein would be repeatedly exposed to new influxes of moisture. The repeated exposure of internal optical surfaces to large amounts of moisture eventually saturates any desiccant located within the telescope. This necessitates dissassembly of the telescope, as before, which is very undesirable. What is needed is a method of absorbing moisture which does not require major disassembly or maintenance of the telescope for continued use.
While evacuation systems or dry gas apparatus might be used to purge the internal atmosphere of a telescope to replace it with "dry" air, this proves far too complex and expensive to provide meaningful protection in the highly portable environment of the telescope art.
Therefore, what is needed is a new type of humidity or moisture control and removal apparatus which is very simple and easy to use, is removable without disassembly of the telescope, is rechargable, and is cost efficient.